The fiberization of molten mineral material such as glass can be accomplished by several known methods. One conventional method is rotary fiberization. At least as early as 1933 it was known to produce glass fibers by centrifugally forcing molten glass through perforations in the periphery of a rapidly rotating spinner or rotor followed by ripping the fibers apart by an annular air current traveling transverse to the emerging fibers, as evidenced by German Pat. No. 571,807. It has also been known, at least since 1940, to make glass fibers purely by the action of a rotary spinner, as shown by U.S. Pat. No. 2,192,944. After leaving the perforations in the periphery of the rotor, the fibers were attenuated somewhat due to their engagement with the relatively quiescent air surrounding the rotor, but, as reported in U.S. Pat. No. 2,431,205, the degree of attenuation caused by this effect is very limited. To increase the degree of attenuation and thus reduce the fiber diameter, this latter patent proposed to anchor the streams or fibers at a point removed from the rotor.
None of the above mentioned references revealed the diameter of the glass fibers produced by the disclosed processes, but later references evidenced that the fiber diameter was at least greater than 5 microns and than was possible using the more costly flame attenuation fiberizing technique, e.g., see U.S. Pat. Nos. 2,609,566 and U.S. Pat. No. Re. 24,708. The former patent proposed to correct this deficiency by subjecting the centrifugally drawn out primary fibers to further attenuation by the action of a transverse blast of hot gas. This gas had to have a temperature and a velocity sufficient to soften and attenuate the primary fibers. The gas blast was provided by the combustion of substantial quanities of fuel to produce a gaseous stream having a velocity of at least 1,200 feet per second and a temperature of at least 3,000.degree. F.
From the issuance of U.S. Pat. No. 2,609,566 in 1952 and until now a large number of advancements have been made in the rotary fiberization field, but none have accomplished the manufacture of glass fibers having an average diameter below 7 microns, and particularly below 5 microns, without the necessity of also using a relatively high temperature gaseous blast to attenuate the primary fibers. It would be highly desirable to eliminate the hot gas blast or equivalent high energy usage attenuation step without sacrificing the desirably small fiber diameter it produces, particularly in view of the energy crisis and the resultant rapid increase in the prices of all fuels. For example, in a typical rotary fiberization process as much as about 7,000 to 8,000 cubic feet of natural gas is required for external jet blast attenuation for every ton of glass fiber produced. In a typical rotary fiberization process making 4-7 micron fibers by forcing the glass through 24 mil orifices in the rotor and attenuating the primary fibers with such a hot gaseous blast, the fiber diameter jumps to 10 to 15 microns when the burners providing the heat for the hot gaseous blast are turned off.
It has also been suggested in U.S. Pat. No. 3,511,306 to make the orifices in the rotor as small as 10 mils to make staple fiber having a diameter of 4 to 10 microns, but it was not recognized that, by carefully controlling the relationship between the process variables, the hot blast attenuation could be eliminated. This reference, typical of the prior art, included hot gas blast attenuation as one of the process steps.
While some of the above prior art processes produce staple fibers having diameters of 7 microns or less, these processes present several problems. The large volume of fuel such as natural gas utilized by such processes is not always readily available and acute shortages are forecast. Consequently, production can be interrupted or slowed by the unavailability of sufficient natural gas for the process.
It is desirable to eliminate the additional expense of providing the blast of hot gases for attenuation plus the maintenance and related problems associated with the burners used in the attenuating apparatus. Also, every fuel burning step produces pollutants that must be dealt with causing an additional operating expense. Finally, the additional heat added by the attenuating burners must be absorbed in the collection chamber prior to felting the staple fiber into a mat and frequently causes premature curing of the binder. This is undesirable and places a restriction on the type of binders that can be used.